Apparently T-Mobile will be using 1700 and 2100 Mhz for LTE and move UMTS over to 1900 Mhz in the near future (source: Fierce Wireless). Would existing T-Mobile UMTS phones start supporting LTE at that point? I know jack about the technology, but I know different phones support different speeds of UMTS/HSPDA+, so it seems too much to ask.